As a conventional technology of this kind, there is one disclosed in Patent Document 1. The conventional technology disclosed in Patent Document 1 is provided with an engine, a variable displacement hydraulic pump drivable by power transmitted from the engine, and a hydraulic actuator drivable by pressure oil delivered from the variable displacement hydraulic pump. In addition, the conventional technology is also provided with an actuator control valve and an exhaust gas purification system. The actuator control valve controls a flow of pressure oil to be fed from the variable displacement hydraulic pump to the hydraulic actuator, and is switchable between a feed state in which the pressure oil delivered from the variable displacement hydraulic pump is to be fed to the hydraulic actuator and a non-feed state in which the pressure oil is returned to a hydraulic oil reservoir without feeding it to the hydraulic actuator. The exhaust gas purification system has a filter for trapping particulate matter in exhaust gas produced from the engine. Further, this conventional technology is also provided with an exhaust gas temperature raising processing means for performing, when the actuator control valve is in the above-mentioned non-feed state and clogging has occurred on the filter of the exhaust gas purification system, processing to increase a load acting on the engine such that a temperature of the exhaust gas is raised to a temperature needed to burn the particulate matter. This exhaust gas temperature raising processing means is configured to include a selector valve, which is openable or closable to communicate or cut off a line through which the pressure oil delivered from the variable displacement hydraulic pump is guided to the hydraulic oil reservoir.
According to this conventional technology, when the actuator control valve is in the non-feed state and clogging has occurred on the filter of the exhaust gas purification system, the selector valve is switchingly controlled to a closed position. As a consequence, the line that connects the variable displacement hydraulic pump and the hydraulic oil reservoir to each other is cut off, so that the pressure in a line section that connects the selector valve and the variable displacement hydraulic pump to each other, in other words, the pump delivery pressure becomes high, and therefore, the load acting on the engine increases. As a result, the temperature of exhaust gas from the engine rises to burn particulate matter contained in the exhaust gas.